linux.git/drivers/video/console/Kconfig, branch v4.16 Linux kernel source tree fbcon: Make fbcon a built-time depency for fbdev 2017-08-01T15:32:07+00:00 Daniel Vetter daniel.vetter@ffwll.ch 2017-08-01T15:32:07+00:00 6104c37094e729f3d4ce65797002112735d49cd1 There's a bunch of folks who're trying to make printk less contended and faster, but there's a problem: printk uses the console_lock, and the console lock has become the BKL for all things fbdev/fbcon, which in turn pulled in half the drm subsystem under that lock. That's awkward. There reasons for that is probably just a historical accident: - fbcon is a runtime option of fbdev, i.e. at runtime you can pick whether your fbdev driver instances are used as kernel consoles. Unfortunately this wasn't implemented with some module option, but through some module loading magic: As long as you don't load fbcon.ko, there's no fbdev console support, but loading it (in any order wrt fbdev drivers) will create console instances for all fbdev drivers. - This was implemented through a notifier chain. fbcon.ko enumerates all fbdev instances at load time and also registers itself as listener in the fbdev notifier. The fbdev core tries to register new fbdev instances with fbcon using the notifier. - On top of that the modifier chain is also used at runtime by the fbdev subsystem to e.g. control backlights for panels. - The problem is that the notifier puts a mutex locking context between fbdev and fbcon, which mixes up the locking contexts for both the runtime usage and the register time usage to notify fbcon. And at runtime fbcon (through the fbdev core) might call into the notifier from a printk critical section while console_lock is held. - This means console_lock must be an outer lock for the entire fbdev subsystem, which also means it must be acquired when registering a new framebuffer driver as the outermost lock since we might call into fbcon (through the notifier) which would result in a locking inversion if fbcon would acquire the console_lock from its notifier callback (which it needs to register the console). - console_lock can be held anywhere, since printk can be called anywhere, and through the above story, plus drm/kms being an fbdev driver, we pull in a shocking amount of locking hiercharchy underneath the console_lock. Which makes cleaning up printk really hard (not even splitting console_lock into an rwsem is all that useful due to this). There's various ways to address this, but the cleanest would be to make fbcon a compile-time option, where fbdev directly calls the fbcon register functions from register_framebuffer, or dummy static inline versions if fbcon is disabled. Maybe augmented with a runtime knob to disable fbcon, if that's needed (for debugging perhaps). But this could break some users who rely on the magic "loading fbcon.ko enables/disables fbdev framebuffers at runtime" thing, even if that's unlikely. Hence we must be careful: 1. Create a compile-time dependency between fbcon and fbdev in the least minimal way. This is what this patch does. 2. Wait at least 1 year to give possible users time to scream about how we broke their setup. Unlikely, since all distros make fbcon compile-in, and embedded platforms only compile stuff they know they need anyway. But still. 3. Convert the notifier to direct functions calls, with dummy static inlines if fbcon is disabled. We'll still need the fb notifier for the other uses (like backlights), but we can probably move it into the fb core (atm it must be built-into vmlinux). 4. Push console_lock down the call-chain, until it is down in console_register again. 5. Finally start to clean up and rework the printk/console locking. For context of this saga see commit 50e244cc793d511b86adea24972f3a7264cae114 Author: Alan Cox <alan@linux.intel.com> Date: Fri Jan 25 10:28:15 2013 +1000 fb: rework locking to fix lock ordering on takeover plus the pile of commits on top that tried to make this all work without terminally upsetting lockdep. We've uncovered all this when console_lock lockdep annotations where added in commit daee779718a319ff9f83e1ba3339334ac650bb22 Author: Daniel Vetter <daniel.vetter@ffwll.ch> Date: Sat Sep 22 19:52:11 2012 +0200 console: implement lockdep support for console_lock On the patch itself: - Switch CONFIG_FRAMEBUFFER_CONSOLE to be a boolean, using the overall CONFIG_FB tristate to decided whether it should be a module or built-in. - At first I thought I could force the build depency with just a dummy symbol that fbcon.ko exports and fb.ko uses. But that leads to a module depency cycle (it works fine when built-in). Since this tight binding is the entire goal the simplest solution is to move all the fbcon modules (and there's a bunch of optinal source-files which are each modules of their own, for no good reason) into the overall fb.ko core module. That's a bit more than what I would have liked to do in this patch, but oh well. Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Reviewed-by: Sean Paul <seanpaul@chromium.org> Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> 
There's a bunch of folks who're trying to make printk less
contended and faster, but there's a problem: printk uses the
console_lock, and the console lock has become the BKL for all things
fbdev/fbcon, which in turn pulled in half the drm subsystem under that
lock. That's awkward.

There reasons for that is probably just a historical accident:

- fbcon is a runtime option of fbdev, i.e. at runtime you can pick
  whether your fbdev driver instances are used as kernel consoles.
  Unfortunately this wasn't implemented with some module option, but
  through some module loading magic: As long as you don't load
  fbcon.ko, there's no fbdev console support, but loading it (in any
  order wrt fbdev drivers) will create console instances for all fbdev
  drivers.

- This was implemented through a notifier chain. fbcon.ko enumerates
  all fbdev instances at load time and also registers itself as
  listener in the fbdev notifier. The fbdev core tries to register new
  fbdev instances with fbcon using the notifier.

- On top of that the modifier chain is also used at runtime by the
  fbdev subsystem to e.g. control backlights for panels.

- The problem is that the notifier puts a mutex locking context
  between fbdev and fbcon, which mixes up the locking contexts for
  both the runtime usage and the register time usage to notify fbcon.
  And at runtime fbcon (through the fbdev core) might call into the
  notifier from a printk critical section while console_lock is held.

- This means console_lock must be an outer lock for the entire fbdev
  subsystem, which also means it must be acquired when registering a
  new framebuffer driver as the outermost lock since we might call
  into fbcon (through the notifier) which would result in a locking
  inversion if fbcon would acquire the console_lock from its notifier
  callback (which it needs to register the console).

- console_lock can be held anywhere, since printk can be called
  anywhere, and through the above story, plus drm/kms being an fbdev
  driver, we pull in a shocking amount of locking hiercharchy
  underneath the console_lock. Which makes cleaning up printk really
  hard (not even splitting console_lock into an rwsem is all that
  useful due to this).

There's various ways to address this, but the cleanest would be to
make fbcon a compile-time option, where fbdev directly calls the fbcon
register functions from register_framebuffer, or dummy static inline
versions if fbcon is disabled. Maybe augmented with a runtime knob to
disable fbcon, if that's needed (for debugging perhaps).

But this could break some users who rely on the magic "loading
fbcon.ko enables/disables fbdev framebuffers at runtime" thing, even
if that's unlikely. Hence we must be careful:

1. Create a compile-time dependency between fbcon and fbdev in the
least minimal way. This is what this patch does.

2. Wait at least 1 year to give possible users time to scream about
how we broke their setup. Unlikely, since all distros make fbcon
compile-in, and embedded platforms only compile stuff they know they
need anyway. But still.

3. Convert the notifier to direct functions calls, with dummy static
inlines if fbcon is disabled. We'll still need the fb notifier for the
other uses (like backlights), but we can probably move it into the fb
core (atm it must be built-into vmlinux).

4. Push console_lock down the call-chain, until it is down in
console_register again.

5. Finally start to clean up and rework the printk/console locking.

For context of this saga see

commit 50e244cc793d511b86adea24972f3a7264cae114
Author: Alan Cox <alan@linux.intel.com>
Date:   Fri Jan 25 10:28:15 2013 +1000

    fb: rework locking to fix lock ordering on takeover

plus the pile of commits on top that tried to make this all work
without terminally upsetting lockdep. We've uncovered all this when
console_lock lockdep annotations where added in

commit daee779718a319ff9f83e1ba3339334ac650bb22
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Sat Sep 22 19:52:11 2012 +0200

    console: implement lockdep support for console_lock

On the patch itself:
- Switch CONFIG_FRAMEBUFFER_CONSOLE to be a boolean, using the overall
  CONFIG_FB tristate to decided whether it should be a module or
  built-in.

- At first I thought I could force the build depency with just a dummy
  symbol that fbcon.ko exports and fb.ko uses. But that leads to a
  module depency cycle (it works fine when built-in).

  Since this tight binding is the entire goal the simplest solution is
  to move all the fbcon modules (and there's a bunch of optinal
  source-files which are each modules of their own, for no good
  reason) into the overall fb.ko core module. That's a bit more than
  what I would have liked to do in this patch, but oh well.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
video: console: Remove reference to CONFIG_8xx 2017-04-21T14:56:10+00:00 Christophe Leroy christophe.leroy@c-s.fr 2017-04-21T14:56:10+00:00 3bbb5b8234161db431992e5d1f8b7cb88ad9dec3 CONFIG_8xx is deprecated and should soon be removed in favor of CONFIG_PPC_8xx. Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> Cc: "David S. Miller" <davem@davemloft.net> Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> 
CONFIG_8xx is deprecated and should soon be removed in favor
of CONFIG_PPC_8xx.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
console: Make persistent scrollback a boot parameter 2017-01-25T10:54:02+00:00 Manuel Schölling manuel.schoelling@gmx.de 2017-01-13T20:07:58+00:00 1a336c934623b011c289a298aff3b7fdefb3f876 The impact of the persistent scrollback feature on the code size is rather small, so the config option is removed. The feature stays disabled by default and can be enabled by using the boot command line parameter 'vgacon.scrollback_persistent=1' or by setting VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT=y. Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de> Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
The impact of the persistent scrollback feature on the code size is
rather small, so the config option is removed. The feature stays
disabled by default and can be enabled by using the boot command line
parameter 'vgacon.scrollback_persistent=1' or by setting
VGACON_SOFT_SCROLLBACK_PERSISTENT_ENABLE_BY_DEFAULT=y.

Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
Suggested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
console: Add persistent scrollback buffers for all VGA consoles 2017-01-25T10:54:02+00:00 Manuel Schölling manuel.schoelling@gmx.de 2017-01-13T20:07:57+00:00 aabd31c421ddc730edf6d89c4ed3885e4fca5e30 Add a scrollback buffers for each VGA console. The benefit is that the scrollback history is not flushed when switching between consoles but is persistent. The buffers are allocated on demand when a new console is opened. This breaks tools like clear_console that rely on flushing the scrollback history by switching back and forth between consoles which is why this feature is disabled by default. Use the escape sequence \e[3J instead for flushing the buffer. Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de> Reviewed-by: Andrey Utkin <andrey_utkin@fastmail.com> Tested-by: Andrey Utkin <andrey_utkin@fastmail.com> Tested-by: Adam Borowski <kilobyte@angband.pl> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
Add a scrollback buffers for each VGA console. The benefit is that
the scrollback history is not flushed when switching between consoles
but is persistent.
The buffers are allocated on demand when a new console is opened.

This breaks tools like clear_console that rely on flushing the
scrollback history by switching back and forth between consoles
which is why this feature is disabled by default.
Use the escape sequence \e[3J instead for flushing the buffer.

Signed-off-by: Manuel Schölling <manuel.schoelling@gmx.de>
Reviewed-by: Andrey Utkin <andrey_utkin@fastmail.com>
Tested-by: Andrey Utkin <andrey_utkin@fastmail.com>
Tested-by: Adam Borowski <kilobyte@angband.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
openrisc: prevent VGA console, fix builds 2016-12-12T14:10:29+00:00 Randy Dunlap rdunlap@infradead.org 2016-11-20T23:40:32+00:00 7c7808ce107d63e158dbbc3af085980985a0c3c4 OpenRISC does not support VGA console, so prevent that kconfig symbol from being enabled for OpenRISC, thus fixing these build errors: drivers/built-in.o: In function `vgacon_save_screen': vgacon.c:(.text+0x20e0): undefined reference to `screen_info' vgacon.c:(.text+0x20e8): undefined reference to `screen_info' drivers/built-in.o: In function `vgacon_init': vgacon.c:(.text+0x284c): undefined reference to `screen_info' vgacon.c:(.text+0x2850): undefined reference to `screen_info' drivers/built-in.o: In function `vgacon_startup': vgacon.c:(.text+0x28d8): undefined reference to `screen_info' drivers/built-in.o:vgacon.c:(.text+0x28f0): more undefined references to `screen_info' follow Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Reported-by: kbuild test robot <fengguang.wu@intel.com> Cc: Chen Gang <gang.chen@asianux.com> Cc: Jonas Bonn <jonas@southpole.se> Signed-off-by: Stafford Horne <shorne@gmail.com> 
OpenRISC does not support VGA console, so prevent that kconfig symbol
from being enabled for OpenRISC, thus fixing these build errors:

   drivers/built-in.o: In function `vgacon_save_screen':
   vgacon.c:(.text+0x20e0): undefined reference to `screen_info'
   vgacon.c:(.text+0x20e8): undefined reference to `screen_info'
   drivers/built-in.o: In function `vgacon_init':
   vgacon.c:(.text+0x284c): undefined reference to `screen_info'
   vgacon.c:(.text+0x2850): undefined reference to `screen_info'
   drivers/built-in.o: In function `vgacon_startup':
   vgacon.c:(.text+0x28d8): undefined reference to `screen_info'
   drivers/built-in.o:vgacon.c:(.text+0x28f0): more undefined references to `screen_info' follow

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Cc: Chen Gang <gang.chen@asianux.com>
Cc: Jonas Bonn <jonas@southpole.se>
Signed-off-by: Stafford Horne <shorne@gmail.com>
Merge tag 'fbdev-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/tomba/linux 2015-09-08T23:42:55+00:00 Linus Torvalds torvalds@linux-foundation.org 2015-09-08T23:42:55+00:00 fa815580fb87d1b8c218f9eba8122b2fc3f1a68c Pull fbdev updates from Tomi Valkeinen: "Minor fixes and cleanups" * tag 'fbdev-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/tomba/linux: video: fbdev: atmel_lcdfb: remove useless include video: fbdev: pxa168fb: Use devm_clk_get fbdev: ssd1307fb: fix error return code fbdev: fix snprintf() limit in show_bl_curve() video: fbdev: s3c-fb: Constify platform_device_id video: fbdev: atmel: fix warning for const return value video: fbdev: Drop owner assignment from platform_driver video: fbdev: Drop owner assignment from i2c_driver fbdev: remove unnecessary memset in vfb framebuffer: disable vgacon on microblaze arch fbdev: udlfb: remove unneeded initialization in few places fbdev: Allow compile test of GPIO consumers if !GPIOLIB fbdev: fix cea_modes array size 
Pull fbdev updates from Tomi Valkeinen:
 "Minor fixes and cleanups"

* tag 'fbdev-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/tomba/linux:
  video: fbdev: atmel_lcdfb: remove useless include
  video: fbdev: pxa168fb: Use devm_clk_get
  fbdev: ssd1307fb: fix error return code
  fbdev: fix snprintf() limit in show_bl_curve()
  video: fbdev: s3c-fb: Constify platform_device_id
  video: fbdev: atmel: fix warning for const return value
  video: fbdev: Drop owner assignment from platform_driver
  video: fbdev: Drop owner assignment from i2c_driver
  fbdev: remove unnecessary memset in vfb
  framebuffer: disable vgacon on microblaze arch
  fbdev: udlfb: remove unneeded initialization in few places
  fbdev: Allow compile test of GPIO consumers if !GPIOLIB
  fbdev: fix cea_modes array size
drivers/video/concole: add negative dependency for VGA_CONSOLE on ARC 2015-09-04T23:54:41+00:00 Yuriy Kolerov yuriy.kolerov@synopsys.com 2015-09-04T22:42:58+00:00 031e29b5877f31676739dc2f847d04c2c0732034 Architectures which support VGA console must define screen_info structurture from "uapi/linux/screen_info.h". Otherwise undefined symbol error occurs. Usually it's defined in "setup.c" for each architecture. If an architecture does not support VGA console (ARC's case) there are 2 ways: define a dummy instance of screen_info or add a negative dependency for VGA_CONSOLE in to prevent selecting this option. I've implemented the second way. However the best solution is to add HAVE_VGA_CONSOLE option for targets which support VGA console. Then turn off VGA_CONSOLE by default and add dependency to HAVE_VGA_CONSOLE. But right now it's better to just add a negative dependency for ARC and then consider how to collaborate about this issue with maintainers of other architectures. Signed-off-by: Yuriy Kolerov <yuriy.kolerov@synopsys.com> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com> Cc: Jaya Kumar <jayalk@intworks.biz> Cc: Vineet Gupta <vgupta@synopsys.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> 
Architectures which support VGA console must define screen_info
structurture from "uapi/linux/screen_info.h".  Otherwise undefined
symbol error occurs.  Usually it's defined in "setup.c" for each
architecture.

If an architecture does not support VGA console (ARC's case) there are 2
ways: define a dummy instance of screen_info or add a negative
dependency for VGA_CONSOLE in to prevent selecting this option.

I've implemented the second way.  However the best solution is to add
HAVE_VGA_CONSOLE option for targets which support VGA console.  Then
turn off VGA_CONSOLE by default and add dependency to HAVE_VGA_CONSOLE.
But right now it's better to just add a negative dependency for ARC and
then consider how to collaborate about this issue with maintainers of
other architectures.

Signed-off-by: Yuriy Kolerov <yuriy.kolerov@synopsys.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Jaya Kumar <jayalk@intworks.biz>
Cc: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
framebuffer: disable vgacon on microblaze arch 2015-08-20T07:53:25+00:00 Nicolai Stange nicstange@gmail.com 2015-06-17T19:40:33+00:00 48fd8ecf29e3c1199432e173858f5ca4bc529738 Fix an allmodconfig link failer on microblaze: drivers/built-in.o: In function `vgacon_save_screen': drivers/video/console/.tmp_vgacon.o:(.text+0x8fc10): undefined reference to `screen_info' Disable vgacon on microblaze because the symbol struct screen_info screen_info; is not defined for the microblaze arch. Signed-off-by: Nicolai Stange <nicstange@gmail.com> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com> 
Fix an allmodconfig link failer on microblaze:
  drivers/built-in.o: In function `vgacon_save_screen':
  drivers/video/console/.tmp_vgacon.o:(.text+0x8fc10):
    undefined reference to `screen_info'

Disable vgacon on microblaze because the symbol
  struct screen_info screen_info;
is not defined for the microblaze arch.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
console/dummy: Move screen size selection from CPP to Kconfig 2015-01-13T12:54:48+00:00 Geert Uytterhoeven geert@linux-m68k.org 2015-01-12T20:17:02+00:00 8f5b1e6511b83ab5483dc5f8b60e2438e9c6dfbe PA-RISC already handled the dummy console screen size selection in Kconfig, so generalize this to other platforms. ARM keeps on using screen_info, which is filled in by platform-specific code, or from ATAGS. Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com> 
PA-RISC already handled the dummy console screen size selection in
Kconfig, so generalize this to other platforms.

ARM keeps on using screen_info, which is filled in by
platform-specific code, or from ATAGS.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
video: vgacon: Don't build on arm64 2014-01-17T08:57:45+00:00 Mark Brown broonie@linaro.org 2013-12-17T23:37:01+00:00 ee23794b86689e655cedd616e98c03bc3c74f5ec arm64 is unlikely to have a VGA console and does not export screen_info causing build failures if the driver is build, for example in all*config. Add a dependency on !ARM64 to prevent this. This list is getting quite long, it may be easier to depend on a symbol which architectures that do support the driver can select. Signed-off-by: Mark Brown <broonie@linaro.org> [tomi.valkeinen@ti.com: moved && to first modified line] Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com> 
arm64 is unlikely to have a VGA console and does not export screen_info
causing build failures if the driver is build, for example in all*config.
Add a dependency on !ARM64 to prevent this.

This list is getting quite long, it may be easier to depend on a symbol
which architectures that do support the driver can select.

Signed-off-by: Mark Brown <broonie@linaro.org>
[tomi.valkeinen@ti.com: moved && to first modified line]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>